1. Field of the Invention
The invention relates to an antenna and, more particularly, to a triple band antenna.
2. Description of the Related Art
In recent years, wireless communication standards are closely integrated into mobile devices. For example, a mobile phone, a hand-held game, a MP3, a MP4, a PMP, a mobile TV, a GPS and a peripheral control device are integrated with a plurality of wireless standards such as the Wi-Fi standard, and they greatly need embedded antennas, and therefore, miniature antennas are essential components for embedded mobile applications.
The design tendency is to be thin besides miniature. As for a 3C products on the market, such as a mobile phone, a common portable intelligent device and a consumer electronic product, fashionable, thin and light factors are gradually taken into account when consumers buy products, and therefore, antennas for mobile applications are intended to be designed to be miniature, thin and embedded even intelligent and multi-band in the future.
The so-called miniature antenna is a microstrip antenna for meeting with the new tendency caused by the application requirement of portable and hand-held devices. Generally speaking, the miniature antennas mostly are planar antennas or array planar antennas with a plurality of plates, and they also may be designed in other mode such as a slot design mode.
Generally speaking, the antennas used in miniature structures include a planar inverted F antenna (PIFA), a unipole antenna and a dipole antenna. For example, as for a mobile phone, the miniature antenna structure commonly used in the mobile phone is a dipole antenna. Although the miniature antenna structure is a type of dipole antenna, the shape of the miniature antenna structure is greatly changed to reduce the volume of the miniature antenna structure. The miniature antenna structure may be circular, elliptic, rectangular or trigonal to allow the antenna unit to be further slim, light, small and short.
Additional miniature antenna structures that are not integrated with application circuits include a patch antenna, a surface mountable antenna and a helical antenna. The embedded mode often utilizes the PIFA in recent years, and this type of antenna has a short circuit structure for reducing the resonance length of the antenna from a half to a quarter, and then the antenna is further smaller.
FIG. 1 is a schematic diagram showing a conventional dual-band antenna. A dual-band antenna 10 includes a feed-in portion 101, a high-frequency radiating portion 102, a low-frequency radiating portion 103 and a grounding portion 104. The high-frequency radiating portion 102 extends from the feed-in portion 101, the low-frequency radiating portion 103 extends from the feed-in portion 101, and the grounding portion 104 is connected to the low-frequency radiating portion 103 and the high-frequency radiating portion 102.
The dual-band antenna is inadequate due to the development of the WIMAX technology, which reflects the importance of the triple band antenna. Therefore, a triple band with a broad operating bandwidth, a small volume and a simple structure is an important development objective of the antenna technology in the future.